Wastewater lagoons or stabilization ponds provide the simplest and the oldest wastewater treatment for municipal and industrial wastewaters which support bacteriological activity and decomposition, and reduction of organic matter.
Wastewater lagoons are primarily used for wastewater treatment by small municipalities and industries, where adequate land is available.
Wastewater lagoons are typically known as conventional lagoons and aerated lagoons.
In the conventional lagoons, aeration of the wastewater is not used and in the aerated lagoons the wastewater is aerated inside the lagoons, for a period of several days to several weeks, depending on the climatic conditions and strength of the wastewater. Air is introduced into the wastewater by air blowers through pipes and air diffusers which are located at the bottom of the lagoons, in a grid pattern, in order to cover the lagoons evenly and adequately. The air diffusers produce air bubbles which vary in size from fine to coarse and which rise from the bottom to the top of the wastewater under static conditions.
The purpose of the aeration is to introduce oxygen into the wastewater which contain aerobic bacteria and which need oxygen for living, reproduction and degradation of organic matter contained in the wastewater.
Another method of the wastewater aeration is by surface mechanical mixers located on the surface of the wastewater or by submerged mechanical mixers c/w air aspirators located in the lower part of the wastewater. Both types of the air-wastewater mixers introduce air into the wastewater under dynamic conditions and produce air bubbles of varying size, quantity and range of dispersion, and efficiency of transfer of oxygen into the wastewater.
Both conventional and aerated lagoons have several essential drawbacks.
The conventional lagoons require a large area, impermeable soil or synthetic plastic or asphalt or concrete liners and are costly to construct. Lagoons which are not watertight may cause serious environmental problems of contamination of soil and ground and surface waters, and become a health hazard. The conventional aerated lagoons are not efficient, require a large area as compared to mechanical/biological wastewater treatment plants, have a high electric power demand and are not suitable for installation in cold climates. Also the equipment located inside the lagoons is difficult and costly to maintain.
The invention is based on aeration of wastewater outside lagoons by means of a wastewater pump and an efficient air aspirator-mixer which renders an economical aeration system and which facilitates maintenance of the aeration equipment, and which lends itself to a flexible design of the aeration treatment system to operate as an activated sludge process in a secondary treatment system, in a tertiary treatment system, or in an extended aeration treatment system.
The invention provides an efficient and economical wastewater treatment system which can operate in warm and cold climates, and which can be used with existing or new lagoons having a single or multi-cell design including anaerobic, primary and secondary cells.
The invention is well suited to treatment of municipal and industrial wastewaters with varying strength and flow rates.
New wastewater treatment facility can be provided with a small lagoon having retention time of several days to several weeks in order to store settled solids and to provide daily flow balancing of incoming wastewater, and to provide adequate clarification of treated wastewater for a continuous discharge of the treated wastewater to the environment throughout the year, without a seasonal storage.
The wastewater aeration treatment system, according to the invention, requires a small building to house the aeration equipment and small tanks which are optional for installations in cold climates.